Case hardened malleable casting and process for making the same



July 1944. J. H. POWERS 2,354,055

CASE HARDENED MALLEABLE CASTING AND PROCESS FOR MAKING THE SAME FiledMarch 24, 1942 A Inventor; J mes H. owers,

His Attorney Patented Ju1 '1s,1944

CASE HARDENED MALLEABLE CASTING AND PROCESS FOR MAKING THE SAME James H.Powers, Fort Wayne, Ind., assignor to' General Electric Company,

New York a corporation of Application March 24, 1942, Serial No. 435,9266 Claims. (Cl. 148-2155) The present invention is a case hardenedmalleable iron casting and a process for heat treating malleable ironcastings whereby the surfaces of such castings are hardened andtoughened to such an extent that they are suitable for use as shreddingelements in electrically operated garbage disposal units. Hitherto theseunits generally have employed sintered hard metal compositions of thecharacter disclosed in Schroter Reissue Patent No. 17,624 as theshredding medium. While cemented carbides are satisfactory for thatpurpose they are far more expensive than surface hardened malleableiron.

It is one of the objects of my invention to provide a surface hardenedmalleable iron casting having a hard, deep case. A further object is theprovision of a surface hardened malleable casting which may bemanufactured economically and which is suitable for use as a shreddingelement in a garbage disposal unit.

The novel features which are characteristic of my invention are setforth with particularity in the appended claims. My invention howeverwill best be understood from reference to the following specificationwhen considered in connection with the accompanying drawing in which thesingle figure is a perspective view of the shredding element of agarbage disposal unit embodying the features of the present invention.

The unit comprises a casting I provided on its inner surface withcircumferentially spaced integral projecting portions 2 each of whichgradually increases in thickness towards its lower edge. The lower edge3 and side portion 4 of each projection serve to effect the shreddingoperation in a manner well known in the art and disclosed in mycopending application Serial No. 393,227, filed May 13, 1941, whichbecame Patent No. 2,322,058 on June 15, 1943.

In order to make a malleable casting suitable for use as a shreddingelement it is necessary to increase its tensile strength, wearresistance and hardness. These results as well as improvements in impactresistance and corrosion resistance are secured by the addition of asmall quantity of alloying ingredients and by a heat treatment whichdevelops maximum physical properties in the alloy.

In carrying out the present invention a casting is employed which,before malleabilization, contains the following ingredients inapproximately the percentages indicated:

Per cent 'Carbon 2.30 to 2.50 Silicon .90 to 1.10 Manganese .70 to .90Molybdenum .50 to 1.10 Copper .40 to .60 Chromium .20 to .30 Phos horus.18 maximum Sulphur .12 maximum The malleabilizing operation reduces thecarbon content of the alloy to about .80 to 1.10%. The free carboncontent of the alloy is more greatly reduced in a thin section than in athick section during the malleabilizing process and in castings about 1%of an inch thick the carbon content is reduced to about .80 to .90%.After being malleabilized the casting is heated to a temperature ofabout 1600 F. for a period of time which may vary from about minutes toabout 1 hour and 15 minutes, or long enough to effect a condition ofsolution in the surface portion of the casting. The heating preferablyis carried out in a liquid bath furnace which prevents decarburizing ofthe casting during the high temperature heat treatment. A suitableliquid bath furnace of this type is known in the trade as the Holdenfurnace. The casting is quenched, preferably in oil, from thetemperature of 1600 F. to a temperature of about 650 F. While thecasting might be quenched to room temperature it has been found that ifthe casting is quenched only to a temperature of about 650 F. it isharder and tougher than if quenched to room temperature. If the castingis quenched inch to room temperature a hardness of about 52 to 56 isobtained on the Rockwell C scale. On the other hand, if the casting isquenched from about 1600 F. to about 650 F. the resulting hardness isabout 62 to 71 or more on the Rockwell C scale. Ordinarily, it would beexpected that warpage and cracking would be relieved by an arrestedquench but on the same basis it would be expected that the hardnesswould be reduced and not increased as indicated above. After quenchingto 650 F. the casting is drawn or tempered in a furnace heated to atemperature of about 400 F. and kept in the furnace for about two hoursafter which it may be cooled in air to room temperature.

The casting employed as the shredding element in a garbage disposal unitis about 9. of an inch thick. After the above heat treatment the castinghas a uniform, flne grained, hard, martensitic outer structure of deeppenetration, for example about .040 to .050 inches and a central corewhich consists of relatively large globules of uncombined graphite ortemper carbon characteristic of malleable iron. There is no sharp lineof demarcation between the core and the outer hard case but rather agradual fading out of the very dense case structure from the surface tothe core of the casting.

The castings maybe machined easily and cost relatively little incomparison with steel castings or castings employing hard carbideshredding inserts or elements. The depth or the case and the high degreeof hardness obtained by my improved process are believed to be quiteunusual. For example, in high grade heat treated steels, it is difllcultto obtain a case depth of .03 inch and a hardness about 55 Rockwell Ceven when such steels are alloyed with a relatively high percentage oftungsten.

Manganese in the precentage indicated improves the hardness andtoughness of the casting, Molybdenum improves its tensile and impactstrength as well as its hardness and wear resistance. Copper increasesthe density and tensile strength of the casting and also improves itsWear and corrosion resistance. The chromium may be omitted if desiredbut when present in the small percentage indicated provides somewhatimproved resistance to wear. While I may employ a molybdenum content inthe alloy which varies from about .50 to 1.10%, I prefer to employ apercentage of molybdenum varying from about .90 to 1.10%.

A particular advantage of the casting produced by my process is that itmay be poured to provide relatively thin sections, for example a sectionof about s of an inch thick which is hard and strong. The same castingif made of steel would require a wall thickness of about of an inchinstead of about 1 g of an inch.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A casting containing about .80 to 1.10% carbon, about .90 to 1.10%silicon, about .70 to .90% manganese, about .50 to 1.10% molybdenum,

bon, about .90 to 1.10% silicon, about .70 to .90%

manganese, about .90 to 1.10% molybdenum,

about .40 to .60% copper with the remainder substantially all iron, saidcasting having a case about .04 to .05 inch thick and a hardness ofabout 62 to 71 or more on the Rockwell C scale.

3. A casting containing about .80 to .90% carbon, about .90 to 1.10%silicon, about .70 to .90% manganese, about .90 to 1.10% molybdenum,about .40 to .60% copper, about .20 to .30% chromium with the remaindersubstantially all iron, said casting having a. case at least .04 inchthick and a hardness of about 62 to 71 or more on the Rockwell C scale.

4. The method of hardening the surface of a malleable iron castingcontaining about .80 to 1.10% carbon, about .90 to 1.10% silicon, about.70 to .90% manganese, about .50 to 1.10% molybdenum, about .40 to .60%copper with the remainder substantially all iron which comprises heatingthe casting at a temperature of about 1600 F., quenching the casting toa temperature of about 650 F. and then drawing the casting at a.temperature of about 400 F.

5. The method of hardening the surface of a malleable iron castingcontaining about .80 to 1.10% carbon, about .90 to 1.10% silicon, about.70 to .90% manganese, about .50 to 1.10% molybdenum, about .40 to .60%copper with the remainder substantially all iron, which comprisesheating the casting at about 1600 F. for about 45 to 75 minutes,quenching the casting to about 650 F., and thereafter drawing thecasting at about 400 F. for about two hours.

6. A shredding element for a garbage disposal unit, said elementcomprising a casting'containing about .80 to 1.10% carbon, about .90 to1.10% silicon, about 0.7 to 0.9 manganese, about .50 to 1.10%molybdenum, about .40 to .60% copper with the remainder substantiallyall iron, said casting having a case provided with projecting integralmeans for efiecting the shredding operation, said case having athickness of at least .04 and a hardness of 62 to 71% or more on theRockwell C scale.

JAMES H. POWERS.

CERTIFICATE OF CORRECTION. Patent No. 2,5 1+,o55. ly 18, 191m.

' JAMES H. PWERS.

It is hereby,' certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,first column, line 21;., for the Word "about" read --above--; and secondcolumn, line [4.5, for "0.9" read --O.9%--; and that the said LettersPatent. should be read with this correction therein that the same mayconform to the record of the case in the Patent Office.

Signed and sealed this 26th day of September, A. D. 191414.

Leslie Frazer (Seal) Acting Commissioner of Patents.

